Pressure Vacuum Relief Valve

The pressure&vacuum relief valve is a protection device mounted on a nozzle opening on the top of a fixed roof atmospheric storage tank. Its primary purpose is to protect the tank against rupturing or imploding. Without an opening or a controlled opening. a fixed roof atmospheric tank would rupture under increasing pressure caused by pumping liquid into the tank or as a result of vapor pressure changes caused by severe thermal changes.
Imploding, or the collapsing of a tank, occures during the pumping out procedure or thermal changes. As the liquid level lowers, the vapor space pressure is reduced to below atmospheric pressure. this vacuum condition must be alleviated through a controlled opening on the tank. In short, the tank needs to breathe in order to eliminate the posiibility of rupturing or imploding. Because of its primary function, a Pressure/ Vacuum vlave is commonly referred to as a “ breather valve “
• Pressure Relief : As the pressure in the storage tank increases, the vacuum pallet is held shut. When the set pressure is reached, the pressure pallet lifts and relieves to atmosphere. (or to a header if it a pipe away valve)
• Vacuum Relief : As a vacuum is drawn in the storage tank (for example, when fluid is being pumped out), the pressure pallet is held shut by atmospheric pressure. When the vacuum setting is reached, the pallet lifts and air is drawn in from the atmosphere.